1. Field of the Invention
The present invention relates to a roll having a light weight and a high rigidity. More particularly, the present invention relates to a delivery roll, guide roll or printing roll for use during the processing of a film, foil, paper, cloth or the like.
2. Description of the Related Art
Rolls formed of steel or aluminum are widely used as delivery rolls for films, foils, papers, cloths and the like. Aluminum rolls are mainly used in this field because the specific gravity is small and the specific modulus is low, and rolls having a relatively light weight can be manufactured, but since the Young's modulus of aluminum is about 7000 kg/mm.sup.2 and the specific gravity of aluminum is 2.7 g/cm.sup.3, the specific modulus of aluminum is 2.59.times.10.sup.9 mm. In contrast, in the case of rolls formed of carbon fiber composite materials (hereinafter referred to as "CFRP"), when a high-tenacity carbon fiber is used, the Young's modulus in the axial direction is 8000 to 10000 kg/mm.sup.2, and when a highly elastic carbon fiber is used, the Young's modulus is 13000 to 16000 kg/mm.sup.2, although these values differ to some extent according to the fiber lamination angle and the kind of resin used. The specific gravity of CFRP is as small as 1.5 to 1.6 g/cm.sup.3, and accordingly, the specific modulus is (5 to 10).times.10.sup.9 mm, i.e., about 2 to about 4 times the specific modulus of aluminum.
Therefore, rolls utilizing the above-mentioned advantageous properties of CFRP have been proposed in, for example, GB2020699A, GM8406019, Japanese Examined Patent Publication No. 59-45843,and Japanese Unexamined Patent Publication No. 61-194197.
According to the teaching of Japanese Examined Patent Publication No. 59-45843, carbon fiber prepregs are arranged in the axial direction of a roll shell formed of an aluminum tube and bonded to the inner circumferential surface of the shell, whereby the entire weight of the roll is reduced and the rigidity is increased. Nevertheless, due to structural limitations, a satisfactory reduction of the weight or satisfactory improvement of the rigidity is difficult to obtain.
Japanese Unexamined Patent Publication No. 61-217566 teaches that a roll base is formed from a carbon fiber composite material and a surface treatment is carried out on this roll base to enable a metal flame spraying and metal deposition thereon. This technique is intended to reduce the weight, increase the rigidity, and maintain a high surface strength and hardness of the roll. Since the roll base is composed of the carbon fiber composite material having a high rigidity and a small specific gravity, the weight is sufficiently reduced, and since the surface is tightly covered with a metal, a roll having a high hardness is obtained. Nevertheless, although this roll is very advantageous in these points, the fiber lamination structure is not mentioned or taken into consideration in this proposal, and therefore, further investigations are required into the carbon fiber-winding structure.
More specifically, the carbon fiber has a highly anisotropic Young's modulus and linear expansion coefficient and therefore, if the lamination is based only on the manifestation of the Young's modulus, an unbalanced stress is produced in the interior of the lamination structure, and in an extreme case, cracking occurs. Further, a problem arises of the precision of a molded article, especially the linear precision after peripheral machining, and therefore, an appropriate lamination structure must be selected in view of these problems. Furthermore, molded articles are generally used after certain surface treatments have been conducted, and thus a problem arises of the compatibility with a surface-treating material, especially in connection with the linear expansion coefficient. Namely, in the case of a CFRP roll, it is necessary to specify the linear expansion coefficient in each direction at respective parts and determine a specific lamination method ensuring such linear expansion coefficients, although this need not be taken into consideration in the case of a metal roll.